Research On Microscopic Surface Testing Based On Microdeflectometry

Small-dimension optics such as freeform surfaces,microstructural elements,and other micro-devices,with the advantage of light-weight,flexible design,arraying and large-scale replication,has been extensively applied in various fields of modern optics(e.g.,display,illumination,imaging).However,owing to the limitation of current measurement technology in large dynamic range,it remains a challenge to realize the accurate measurement of free-form surfaces,especially the optics with small area.Deflectometry,with the advantages of simple structure,brief measurement process,high accuracy and large measurement dynamic range,provides a feasible research direction for various small free-form surface measurement.The article mainly includes the following contents:In this paper,the significance of high-precision microscopic surface testing technology with large dynamic range in the development of modern optical system was discussed.Based on the research status of microscopic surface testing technology,a microscopic surface testing system with large slope dynamic range and high accuracy was explained.An on-axis microscope system based on deflectometry was proposed,and the system model was established for system structure error analysis.Then,extra aberration introduced by various system geometric error was analyzed in detail.Owing to the system modeling uncertainties,a calibration method based on computer-aided reverse optimization was proposed.The simulation and analysis were carried out,the RMS value of the surface residual error was 0.0033 μm with system calibrated,the feasibility of the proposed system and corresponding system calibration method was demonstrated.The calibration technology and correction method of the system were studied.The exit light wavelength and nonlinear of the LCD screen were calibrated,and the gray response was corrected.The imaging model of the camera was analyzed,the intrinsic and extrinsic parameters of the camera lens were calibrated,and the distortion correction was completed.An experimental system was established according to the proposed on-axis microscope system,and was used for the measurement of the roughness and surface shape of a convex mirror.The testing results were both compared with Wyko profilometer,RMS deviation of the surface error testing result by the two system was0.0047 μm,the experiment results show that the proposed method is feasible and accurate.A large slope dynamic range surface measurement was also achieved in the extra steep surface testing,compared with a Mirau microscope.